Project Summary/Abstract Periodontal disease affects up to 47% of the adult population in some form and is linked to a number of serious systemic diseases. Despite the significant health and economic burden of periodontal disease, much remains unknown about the effect of the dysbiotic bacterial community and immune response in the oral cavity. Treponema denticola, along with Tannerella forsythia and Porphyromonas gingivalis, compose the ?red complex? of bacteria, prominently associated with severe periodontal disease. The major outer sheath protein (Msp) of T. denticola is known to dysregulate functions of host cells, including neutrophils. Neutrophils are key cells of the body's innate line of defense against pathogens in the gingival tissue, yet during periodontal disease, they are rendered ineffective. Regulation of phosphoinositides (PIPs), important cellular lipid metabolites, through appropriate lipid kinase and phosphatase activity are crucial to orchestrating neutrophil function and driving the immune response. Msp upsets the cellular PIP balance through inhibition of PI3K and activation of the phosphatase and tensin homolog (PTEN). Despite being one of T. denticola's most prominent virulence factors, the exact mechanism behind Msp's ability to limit neutrophil chemotaxis by manipulating the PI3K/PTEN lipid metabolism pathway is not well understood. We hypothesize that exposure to Msp, in isolated form or as a component of outer membrane vesicles, will limit neutrophils from responding to T. denticola, but also secondarily to other members of the ?red complex?, promoting bacterial interaction and survival of the polymicrobial biofilm in the oral cavity. The overall objective of this project is to characterize how T. denticola impairs neutrophil function as a means to dysregulate the innate immune response, with the goal to identify the mechanism by which Msp interferes with PI3K signaling and phosphatase activation and characterize how the interaction of Msp with neutrophils supports the dysbiotic bacterial environment of severe periodontal disease. These goals will be accomplished by 1) determining the role of Msp in activating the lipid phosphatase SHIP1 and how Msp interacts with different isoforms of the lipid kinase PI3K to alter normal neutrophil signaling response and 2) characterizing the impact of T. denticola and Msp interaction with neutrophils to alter the ability of neutrophils to respond to other pathogens. This work will fill a gap in knowledge of the pathogenicity of T. denticola and its role in driving the manipulation of the neutrophil response in polymicrobial infections. Furthermore, the mentoring and training plan outlined in this proposal will aid in the attainment of the professional skills necessary to develop a successful independent academic research program in the future.